Fox den????

I went out this morning  to see if I could find my fox’s den. I know it must be near, as a nursing vixen would not travel far from young cubs. In the corner of the field, there is a large oak tree. There is a hole at the base that opens out into a hollow under the roots of this tree. I could just see a further tunnel leading off under this. I could see no evidence of hairs and it did not smell particularly ‘foxy’ around there, but I am posting these photos to see if anyone thinks it looks like a possible den? Please comment on the link below this post. I am going to stand at the window tonight and see if I can see where they are coming into the field from. They usually appear just before it is dark.